Effect of die dimension on extrusion processing parameters (animal feed)
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  • 1. Effect of Die Dimensions on Extrusion Processing Parameters and Properties of DDGS-Based Aquaculture Feeds Nehru Chevanan,' Kasiviswanathan Muthukumarappan, 2'3 Kurt A. Rosentrater, 4 and James L. Julson3 ABSTRACT Cereal Chem. 84(4):389-398 The goal of this study was to investigate the effect of die nozzle dimensions, barrel temperature profile, and moisture Content on DDGSbased extnidate properties and extruder processing parameters. An Ingredient blend containing 40 17'e. distillers dried grains with solubles (DDGS), along with soy flour, corn flour, fish meal, whe y, mineral and vitamin mix, with a net protein content adjusted to 28 0/c was extruded in a single-screw laboratory extruder using seven different die nozzles. Increasing moisture content of the ingredient mix from 15 to 25% resulted in a 2.0. 16.0, 16.3, 22.9. 18.5. 32.5. and 63.7% decrease, respectively, in bulk density, water-solubility index, sinking velocity, L 5. 6*. mass flow rate, and absolute pressure, as well as 11.6. 16.2, and 7% increases, respectively, in pellet durability, water-absorption index, and a. Increasing the temperature from 101) to 140°C resulted in 17.0. 5.9. 35.4. 50.6. 28.8. 33.9, and 33.9% decreases, respectively, in unit density, pellet durability. sinking velocity, absolute pressure. specific mechanical energy, torque, and apparent viscosity, but a 49.1 and 16.9% increase, respectively, in dough temperature and water-absorption index. Increasing the LID ratio of the die nozzle resulted in an increase in bulk density. L* , o*, and torque, but a decrease in unit density, pellet durability, water-absorption index, sinking velocity, h, mass flow rate. dough temperature, and apparent viscosity. As demonstrated in this study, the selection of an appropriate die geometry, in addition to the selection of suitable temperature and moisture content levels, are critical for producing DDGS-based extrudates with optimum properties. Distillers dried grains with solubles (DDGS) typically contain high amounts of protein (23-29%) and low levels of' starch (l--2%) and are thus a possible alternative protein source for aquaculture feeds (Chin et al 1989; Lee et al 1991: Wu et al 1994. 1996). Depending on the species, aquaculture feeds generally require protein contents of 26-50% (Lovell 1989). Consequently, these formulated feeds can contain high quantities of both protein and starch. Floatability of the extrudates is an important quality parameter for aquaculture feeds (Bandyohadhyay and Ranjan 2001: RolI'e et al 2001). The unit density of extrudates, which affects the floatahility, depends on the extent of expansion obtained during extrusion cooking. Expansion can he controlled by changing the type and nature of ingredients used, and by changing the processing conditions in the extruder. In the extrusion industry, starch-based ingredients are often used to obtain puffed products, while proteinbased ingredients are often used to obtain texturized products (Kokini et al 1992). During extrusion processing of starch-based products, the extent of gelatinization occurring inside the barrel plays an important role in determining final extrudate properties. Depending on the extent of gelatinization, the ingredient mix is turned into an elastic melt inside the barrel (Case et al 1992; Sokhey et al 1994; Ihanoglu et al 1996; Ilo et al 1996; Lin et al 2000). When the elastic melt exits through the die, expansion occurs due to the flashing of water vapor, which occurs due to the sudden drop in pressure (Alves et al 1999; Lam and Flores 2003). During the extrusion processing of protein-based products, on the other hand, the ingredient mix becomes more of a plastic melt inside the barrel. The protein can be denatured due to the heat, which results in modifications in the peptide bonds and amino acid chains. When the material exits through the die, it is in a plastic, homogenous state, and a more porous, fibrous textured product generally results, often due to the voids formed by the steam generated during sudden pressure drop (Gwiazda et al 1987; Singh et al 1991; Sandra and Jose 1993). Operation of extruders depends on many factors, including the pressure developed inside the die, slip at the barrel wall, and the degree to which the screw is filled. The combination of these variables, along with the type and composition of raw ingredients used, will affect operational capabilities (Mercier et al 1989). The extruder die plays an important role in affecting the processing conditions as well. For circular dies, nozzle dimensions (i.e., nozzle diameter and length) will affect process conditions and performance (Chinnaswarny et al 1987). The how of dough inside a circular shaped die (Q) is directly proportional to the pressure developed inside the die (AP). and inversely proportional to the apparent viscosity (id) of the dough inside the die. This can be mathematically expressed as 2 Graduate research assistant, South Dakota State University, Brookings, SD 57007. Professor, South Dakota State University, Brookings, SD 57007. Corresponding author. Phone: 605-688-5661. Fax: 605-688-6764, E-mail address: muthukum@sdstate.edu Bioprocess Engineer, North Central Agricultural Research Laboratory, USDA, ARS, Brookings, SD 57006. Mention of a trade name, propriety product or specific equipment does not Constitute a guarantee or warranty by the United States Department of Agriculture and does not imply approval of a product to the exclusion of others that may be suitable, P rofessor, South Dakota State University, Brookings, SD 57007. doi:1 0.1 094/CCHEM-84-4-0389 © 2007 AACC International, Inc. Q =K ( AP/ ud ) ( I) where K is a proportionality factor, which, for a circular die with a nozzle radius of R and nozzle length of L, can be expressed as (Sokhey et al 1997) (2) K=.irR4I8L The rheological and thermodynamic processes occurring inside the die during forming and stretching have decisive effects on the final quality of extruded products (Mercier et al 1989). Apparent viscosity is the most important rheological property that affects final product properties. During extrusion of biologically based l'eed materials, ingredients often transform into a pseudoplastic melt. And the moisture content of the ingredients, as well as cooking temperature, often significantly affect the apparent viscosity and thus the final extrudate properties (Harper 1981; Rosentrater et al 2005; Shukla et al 2005). Therefore, the objective of this study was to investigate the effect of the die nozzle dimensions, barrel temperature profile, and moisture content on the DDGS-based extrudate properties, and extruder processing parameters. MATERIALS AND METHODS Sample Preparation An ingredient blend containing 40% DDGS, along with appropriate quantities of soy flour, corn flour, Menhaden fish meal, whey, vitamin and mineral mix, with the net protein adjusted to 28% was prepared following Chevanan et al (2005a,b). DDGS was provided by Dakota Ethanol LLC (Wentworth, SD) and was Vol. 84, No. 4, 2007 389
  • 2. ground to a particle size of 100 pm using a laboratory grinder (S500 disc mill, Genmills, Clifton, NJ). Corn flour was provided by Cargill Dry Ingredients (Paris, IL), and soy flour was provided by Cargill Soy Protein Solutions (Cedar Rapids, IA). The ingredients were mixed in a laboratory-scale mixer (N50 mixer, Hobart Corporation, Troy, OH) for 10 mm, and then stored overnight at refrigerated conditions (10 ± 1°C) for moisture stabilization. The moisture content of the ingredient mix was adjusted by adding required quantities of water during mixing. Experimental Design The extrusion studies were conducted using a single-screw extruder (Brahender Plasti-Corder. model PL 2000. South Hackensack, NJ), which had a barrel of 317.5 mm. with a length to diameter ratio of 20:1. The die assembly had an internal conical section and a length of 101.6 mm. A screw with a uniform pitch of 9.05 rnni was used in the experiments. The screw had variable flute depth, with the depth at the feed portion of 9.05 mm, and near the die of 3.81 mm. The compression ratio achieved inside the barrel was 3:1. The speed of the screw and the temperature inside the barrel were controlled by a computer control system. The extruder barrel's band heaters allowed the temperature of the feed lone. transition zone in the barrel, and the die section to be controlled. Compressed air cooling was provided in the barrel section as well, but the die section was not cooled. The extruder had a 7.5 HP motor, and the computer system could control the speed of the screw at 0-2 10 rpm (0-22 rad/sec). Experiments were conducted with a full-factorial design using three levels of moisture content (MC) (IS, 20. and 25%, wh); three levels of temperature gradient in the barrel (90-100-100°C, 90-120-120, and 90-140-140'C) hereafter referred to as temperatures of 100, 120, and 140°C. respectively: and seven levels of die geometry with various nozzle length to diameter ratios. The dimensions of the seven different dies used in the experiments are given in Table I. Measurement of Extrudate Properties Unit density (UD). Extrudates were cut with a razor blade into 20-mm lengths. UD was determined as the ratio of mass to the calculated volume of each piece by assuming cylindrical shapes for each extrudate according to Jamin and Flores (1998). Bulk density (BD) was measured using a standard bushel tester (Seedburo Equipment Co., Chicago. IL) following the method prescribed by the USDA (1999). Pellet durability (PD) was determined following ASAE standard method S269.4 DEC01 (1996); 200 g of the extrudates was tumbled inside a pellet durahilty tester (Seedhuro) for 10 min and then hand-sieved through a No. 6 screen. PD was calculated as where Q is the net torque exerted on the extruder drive (N-rn), w is the angular velocity of the screw (rad/sec), and ,n,,.,.,, is the mass flow rate (g/min). Apparent viscosit y (ii) of the dough in the extruder (Pa-see) was calculated by approximating the barrel and screw as a concentric cylinder viscometer. and then incorporating corrections for tapered screw geometry (Rogers 1970; Lo and Moreira 1996; Konkoly 1997; Lam and Flores 2003; Rosentrater et al 2005). The apparent viscosity was determined as the ratio of shear stress (t,) at screw (N/ni 2 ) to the shear rate (y,) at the screw (I /sec) calculated from Equations 5 and 6 (3) Water absorption index (WAI) was determined according to Jones et a! (2000). To determine WAI, 2.5 g of finely ground sample was suspended in 30 mL of distilled water at 30°C in a 50-mi, tarred centrifuge tube. The content was stirred intermittently over TABLE 1 Dimensions of Dies Used in Study Diameter of Nozzle (mm) Length of Nozzle (mm) LID Ratio 3.0 6.0 4.0 2.7 3.0 2.0 3.0 10.0 20.0 13.7 13.0 17,5 14.5 30.0 3.3 3.3 3.4 4.8 5.8 7.3 10.0 390 CEREAL CHEMISTRY Extrusion Processing Parameters The temperature of the ingredient melt at the end of the barrel (TB) was measured with a Type J thermocouple with a range of 0-400°C. The absolute pressure (P) inside the die was recorded with pressure transducer that had it of 0-68.9 MR The teriiperature of the melt in the die (TD) was recorded with a therriiocouple that was integral to the pressure transducer. The net torque () was measured with a torque transducer that had a range of 040,000 m-g. During experimentation, the extrudate samples were collected for 30-sec intervals, and the mass flow rate (MFR) was then calculated (g!nirn). Based on the torque and the mass how rate data, the various processing variables were then determined. Specific mechanical energ y ( SME) (J/g) was calculated accordin- to Harper (1981) and Martelli (1983) as SME = (* W *60)/ fl7(4) 7. PD = ( Mass of pellet after tumbling/Mass of pellet before rumbling) x too Die No. 30 min and then centrifuged at 3,000 x g for 10 mm. The supernatant water was transferred into tarred aluminum dishes. The mass of the remaining gel was weighed, and WA! was calculated as the ratio of gel mass to the sample mass. Water-solubility index (WSJ) was determined as the water-soluble fraction in the supernatant, expressed as percent of dry sample (Jones et al 2000). The WSI was determined from the amount of dried solids recovered by evaporating the resulting supernatant in an oven at 135°C for 2 hr; it was determined as the mass of solids in the extract to the original sample mass (%). Sinking velocit y (SV) was measured following the method adopted by Hiinadri et a! (1993). SV was measured by recording the time takeii for an extrudate 20 mm long to travel from the surface of water to a depth of 425 min a 2,000-mL graduated cylinder. Color of the extrudates was determined using a spectrophotometer (portable model CM 2500d, Minolta Corporation, Ramsey, NJ) using the L-a-b opposable color space. where L* quantifies the brightness, a quantifies redness/greenness, and h* quantifies yellowness/blueness. =)/(2*)r*(cor)2 */) =C5 Q = (2o) wherer, -,rr i s *r2)/(,.2 (r 2 )= w (5) (ôa) the radius correction due to frustum value re, +T.ffJ ? JJ2 +r(, 2 )/3 ,(m) (6b) where r is the effective radius including the screw root radius and half of flight height (in), L is the screw length in the axial direction (,n), C,, is a correction factor for shear stress (5675.4 for the screw used), 'y, is the shear rate at the screw (]/see), r5 is the barrel radius (m), and C., is the correction factor for shear rate (6.31 for the screw used). Statistical Analysis The measurements were completed in triplicate for all extrudate properties and extrusion processing parameters, except for pellet durability, which was measured in duplicate. The data were
  • 3. then analyzed with Proc GLM to determine the main and interaction effects and LSD using a = 0.05 for comparison, with SAS v.8 software (SAS Institute, Cary, NC). To determine the effect of nozzle length (L), nozzle diameter (D), and length to diameter ratio (L/D) on individual response variables, multiple linear regression analysis was conducted with linear quadratic models Response =Ii + a * D + 02 MC + a 1 * T+a4 * I) * T+ a D * MC+a (, * 1 * MC+a 7 */)2+a5 MCI +a972 (7) Response = 12 + b, * L + h 2 MC + h 3 * T + b4 * L * T+ b 5 * L ,MC+h6iMC+b7L2+b5 MCI +h911 (8) Response =/+c 1 *(lJD)+c 2 *MC+csT+c 4* (lJD)*/+cs' (liD) MC+c 5* T * MC+c 7 *(IJD)2+c5 MCI + (9) The Proc Reg procedure in SAS was used to determine the coefficients for each of the terms, and only statistically significant terms were included in the final model using a step-wise selection method. In Equations 7, 8. and 9. J, '2, and 13 are the intercept values; Oi - a. b 1 - h9 , and c 1 - c9 are the regression coefficients for respective terms; D. L. LID. MC . and T represent the diameter (mm), length (mm). length-to-diameter ratio of the die nozzle (-), moisture content (%, wb) of the blend, and temperature (°C), respectively. RESULTS AND DISCUSSION Changing the levels of temperature, moisture content, and die dimensions were each found to have significant effects on all the extrudate properties studied, except for UD, where the effect of moisture content was not significant (Table II). Temperature, moisture content, and die dimensions also significantly affected all extrusion processing parameters as well (Table Ill). Additionally, the interaction effects were also significant (P < 0.05) for all the extrudate properties. except for die*rnoisture content and die* moisture content*temperature for UD, and temperature* moisture content for WSI. The interaction effect of temperature, moisture content, and die dimensions were also significant for all the extrusion processing variables studied. With regression, it was determined that LID, moisture content, and temperature (using Equation 9) predicted all extrudate properties and the extrusion processing parameters with high R2 values compared with L or D alone as the primary geometric parameters (Equations 7 and 8). Hence, regression modeling using L/D as the die geometry parameter was pursued for all subsequent analysis. Extrudate Properties Unit density (UD), which affects floatahility of extrudates, is a very important quality parameter for aquaculturc feed materials. TABLE II Main Treatment Effects on the Ph ysical Properties of Extrudates' Parameter Unit Density (g/cm3) Bulk Density (g/cm3) Water Pellet Durability Absorption Index (%) Water Solubility Index (%) Sinking Velocity (m/sec) Color L Temp profile ("C) 40,92h 0.l0a 17.71 it 2.63c 95.75a 1.03a 0.45h 90-100-I 00 41.39a 17.70a 0.09b 2.90h 0.45a 94.6Ib l.00b 90-120-120 0.07c 39.65c 16.95a 3.13a 87.19c 0.42c 0.88c 90-140-140 Moisture content ('T) 4-4.41a 0.09a 18.33a 2,73c 0.44a 86,95c 0.96a 15 42.39h 0.08b 17.57b 2.88b 92.40h 0.44h 0,96a 20 36.1 3c 0.08c I6,66c 101a 97.04a 0.44b 0.99a 25 D (mm) L/D (-) 39.28c 0.08d 17.03c 2.99a 94.55c 0.43d 0.98ah 3.33 3.0 41,30b 0.12a 17.45h 2.85h 0,48a 85.06e 0.95b 6.0 3.33 40,78h 16.44d 0. lOb 2.96a 87.17d 0.45b 4.0 0.99c 3.43 41.27b 0.07e 17,61h 2.86h 95.06h 0.43d 0.97ab 2.7 4.81 0.08c 41,32h 18.30a 2.95a 95.21h 0.42f 0.98ah 3.0 5.83 38.09d 0.07f 17,34hc 2.84h 97.99a 0.42e 101a 7.25 2.0 0.08d 42,l3a 17.99a 2.78c 94.23c 0.44c 1.02a 3.0 10.00 a' b' 4.30c 4,37h 4.51a I 3.98th 14,06a 13.91b 4.26c 4.32b 4.56a 15.12a 14.33h 12,76c 4.35cd 4.38bcd 4.46b 4.15e 4.31d 4.67a 4.4lbc 13.36e l4,62a 14.13b 13.7 Id l3.90c I 3.76cd l4,17h Values with the same letter in a column for a given factor are not significantly different (P < 0.05). TABLE III Main Treatment Effects on Extrusion Processing Parameters-' Parameter Temp profile (°C) 90-100-100 90-120-120 90-140-140 Moisture content (%) IS 20 25 D (mm) UD (-) 3.0 3.33 3.33 6.0 4.0 3.43 2.7 4.81 3.0 5.83 2.0 7.25 10.00 3.0 Mass Flow Rate (g/min) Torque (N-m) Absolute Apparent SME (Jig) Viscosity (Pa-sec) Pressure (MPa) Dough Temp (Barrel) (°C) Dough Temp (Die) (°C) 139.3c 141.6b 144.8a 74.04a 62.89b 55.24c 430.52a 360.34b 306.66c 4894.37a 4157.66h 3651.55c 10.91a 7.71b 5.38c 102.85c 1l6.82h 127.12a 104.09c 131.14b 155.19a 165.Ia 153.4b 11 1.5c 62.07b 89.12a 41.03c 307.24b 476.70a 305.24b 4103.00b 5890.98a 2712.31c 12.82a 8.02b 4.65c 116.31a I l5.64h 1t4.43c 126.44c 129.25b 132.84a 126.2g 149.2a 145.6b 140.6e 138.5f 144.1c 143.Od 59.05d 54.67e 56.41de 65.06c 57,26de 80.06a 74.47b 364.65c 301.91e 312.73e 367.66c 330.83d 467.51a 471.89b 3903.20d 3614.00e 3728.80de 4300.80c 3784.90de 5292.00a 4922.40b 4.01f 3.94f 5.05c 9.32c 7.91d 11.88b 13.87a 117.05b 105.25d I l7.58ab 118.l5a 114.89c 1t7.55ab t17.84a 136.60a 126.88e 130.77c 132.05b 126.82e 128.82d 12805d Values with the same letter in a column for a given factor are not significantly different (P < 0.05). Vol. 84, No. 4, 2007 391 II
  • 4. Increasing the moisture content of the ingredient mix had no significant effect (P > 0.05) on the UD of the extrudates. However, increasing the temperature from 100 to 140°C resulted in a significant decrease (17%) in UD of extrudates. Many researchers have observed that temperature has an inverse relationship with the apparent viscosity of the ingredient melt inside the barrel and die (Harper et al 1981; Bhattacharya and Hanna 1986), and that higher temperatures typically result in lower apparent viscosity of the melt. When the ingredient melt (at lower viscosities) exits through the die, extrudates tend to expand more and, thus, have reduced UD. Regression analysis for UD resulted in an R2 value 0.65 using LID as the geometric parameter. Model equation 10 predicts the UD of extrudates with L/D. MC, and T (Table V). The negative value for the term containing L/D, within the bounds of the experiment, indicated that there was a general trend of decrease in UD as the LID ratio was increased. Bulk density (BD) is another key property, as it influences storage space required at the processing plant, during shipping, and at animal production facilities. BD depends on the size, shape, and the extent of expansion during extrusion. Increasing temperature had a significant effect on the BD (P < 0.05). The lowest BD (0.319 g/cm 3 ) was recorded at a Tof 140°C, MC of 25%, and L/D of 7.25. The highest RD (0.509 g/cm) was recorded at a T of 120°C, MC of 20%, and L/D of 3.33 (Table IV). Changing the MC of ingredient mix also had a significant effect on the BD (P < 0.05): increasing MC from 15 to 25% resulted in a 2% decrease in BD. The R2 value of the linear quadratic model with L/D as the geometric parameter was 0.62. Model equation 11 predicts BD using L/D, MC, and T (Table V). A positive coefficient for the L/D and (LID ) 2 terms in the model indicate that there was general increasing trend in BD as the L/D ratio was increased. Pellet durability (PD), which is an important quality parameter of feed materials (Rosentrater et al 2005), can indirectly assess the mechanical strength of extrudates. Increasing T resulted in a significant decrease in the PD (P <0.05). The PD at Tof 100°C was 9.8% higher compared with the PD at T 140°C (Table II). Changing the MC of the ingredient mix also had a significant effect on the PD of the extrudates; and PD at 25% MC was 11.9% higher compared with the PD at 15% MC. At higher MC, the temperature of dough at the die was significantly higher as well (Table III). The mechanical strength of extrudates depends on the extent of heat treatment and the relative degree of starch gelatinization that occurs during processing (Colonna et al 1989). Increasing the MC and T synergistically resulted in a higher extent of heat treatment and gelatinization, which resulted in higher PD. The R2 value of the linear quadratic model using liD as the geometric parameter was 0.69. Model equation 12 predicts PD with L/D, MC, and T (Table V). A negative coefficient for the L/D, LID * MC, and (LID)2 terms in the model indicated that there was, in general, a decreasing trend in PD as the LID ratio was increased. The higher PD at lower T is indicated by the negative coefficient of (1.11 - 0.04* MC) for the T term, while the higher PD at higher MC is summarized by the positive coefficient of (0.04 * 7' - 2.31) for the MC term. Water-absorption index (WAI) is related to the extent of starch that has maintained integrity during extrusion processing, and to the molecular breakdown of starch and protein components. WAI is also indirectly related to water-holding capacity, which thus affects product storage stability. T had a significant effect on the WAI (P <0.05); the WAI was 16.9% higher at a T of 140°C compared with the WAI at a Tof 100°C (Table 11). A similar trend was observed by Anderson et al (1969) with extruded corn grits. TABLE IV Treatment Combination Effects on the Extrudate Properties' Property Die Diameter (mm) Unit density (glcm3) 3.0 6.0 4.0 2.7 3.0 2.0 3.0 Bulk density (g/cm3) 3.0 6.0 4.0 2.7 3.0 2.0 3.0 Pellet durability (%) 3.0 6.0 4.0 2.7 3.0 2.0 3.0 Water absorption index (-) 3.0 6.0 4.0 2.7 3.0 2.0 3.0 90-100-1001C LID (.) 15% 20% 90-120.120°C 25% 20% 3.3 3.3 3.4 4.8 5.8 7.3 10.0 0.97612 na 0.95614 0.958- 14 0.8911-17 087 12.17 1.00 1 ' l.02'' 0.994 ( 20.95 7.13 1.1116 1.03 31,05 1.09' 3,3 3.3 3.4 4.8 5.8 7.3 10.0 na na 0.49 0.47460466.8 0.49 04219.21 0.41 21-22 0.48 0.42 1 6.2 00.493 0.43 15- 17 0.4226.2( 0.42 16-20 0.465-7 0459.12 0,467.10 0.402324 0431315 0.451' 0.49 no na 0.511 0.51 1.2 0.47' 0.44 11130467.8 0.431518 na 0.4580.459-12 045112 0.46 3.3 3,3 3.4 4.8 5.8 7.3 10.0 93.601516 98.00 na 83 . 352397.96 99.06" 87 .982292.1316.79 9364'516 9601 9.129665510 96.56611 94 7313.15 96 ,098.1298.42' 9974(2 9942 1.299.411.2 9545(0(4 97.80 99.09 3.3 3.3 3.4 4.8 5.8 7.3 10.0 2.642226 na 2 .6926.242 . 6926.24 2 . 6826.2.7916.22 24927.29 2. 1229 2.6223.27 2 . 82 15.20 2.4627.29 2 .51 2529 2.6521.25 2.5026.29 1.1912 1.1115 0811417 119' 1.12' 1.17 1-4 1.17' 15% 2.761823 2.5175-29 2.92016 2.642327 2.891218 2.572429 2.7319.23 90-140.140°C 25% 0929.16 no 1.0I1' 0994.12 l.02'' 1.01"' 0.96` 30.99412 1.001' 0,9480 1.00 1 ' 0.948(5 0.9942 1.00 1 ' 0.9812 1.08 1-8I.03'° 1.014-11 1.03 3-101.0431() 15% 25% 20% 0.92 no O. 80 00.79 16-17 0929.16 0.75 17 0.939 6o.8911 17 na 0.89 0.99' 0.929- 16 098 5120.91' 0.8512 0939.15 0.99101' 0.83 13-1 0.948 0.75' 0.85'' 0.412(23 0.5023 0.4590 0.4315' 0.431520 0.441214 04316.20 0.421821 no 0466.80457(0 0.43 [4-16 04411' 0.44 1214 0.402223 0.3923 na 0.4313-14 042 1620 0.412223 0.42°° 0.4022.23 0.46 046° 03726 0.3823 0.3227 03924.25 93.0016.18 no 88 . 162290.772021 91 .70 18.20 92 .68 16.18 95.2411-1493.3617 na 91.36 19-20 97494.7 99.771 95 .989292.05 17-20 96.90 96.5l6 97.10 97743.6 95.27'°' 97.6l 95.0712(4 88.3822 na 40.372675.8024 44042587.3022 9263 161991.1320.21 na 91.61 19-20 96 . 56&1935415.16 89 . 882188,3822 97444.8 93.66°' 98.01 96.24712 99.00' 98.3624 9439(4.15 2801621 na 2 . 6323.27 2.8912-18 2.86 14-19 3.13 2.6726.2430'J8-13 2.9111-17 2 .731923 3.02713 2.76 17-23 2.40282.65 22-26 3.093.10 2.9990 3.2025 3.02' 3.312 3.16 2.8116.20 3143.8 na 2 . 93 I63.12 3.02 7-13 3.05'' 2.91 1.83.2923 3.2824 na 3 .085102,9610.15 2 .88 1 3. 19 3.1536 3.491 3192.6 3.03713 3.62' 3046.12 3.027-11 3.29 (continued on next page) Values with the same superscript numbers for a given property are not significantly different (P <0.05); na, data not available. 392 CEREAL CHEMISTRY
  • 5. Changing the MC of the ingredient mix also had a significant effect on the WAI (P < 0.05). Increasing the MC from 15 to 25% resulted in a 16.2% increase in the WAI. Anderson (1982) observed that higher temperatures and higher moisture contents could result in greater starch breakdown and thus increased formation of an expansible matrix, resulting in higher water-holding capacity, which could lead to an increased extrudate WAI. In this study also, higher T and higher MC resulted in higher WAI of the extrudates. The R2 value for the linear quadratic model with L/D as the geometric parameter was 0.65. Regression equation 13 predicts WAI with L/D, MC, and T (Table V). The negative coefficient for the L/D term in the model indicated that there was a general decreasing trend in WAI as L/D ratio increased. Higher WAI at higher MC and higher T are indicated by the positive coefficients for MC and T terms in the model. Water-solubilitv index (WSJ) is directly related to the extent of starch gelatinization that occurs inside the extruder (Harper 1981). Generally, WSJ increases as the temperature increases, due to starch depolymerization, which leads to reduced length of amylose and aniylopectin chains (Anderson et a! 1982). In our experiments using DDGS. changing T did not result in significant changes in the WSJ of the extrudates. But changing MC did have a signilicant effect. William et al (1977) observed drier conditions of the ingredients affected the extent of dextrinization of starch, which resulted in higher extrudate WSJ. Similarly, in this study the WSJ at 15% MC was 16.0% higher compared with the WSI at 25% MC. The R2 value with LID as the geometric parameter in the linear quadratic model was 0.41. Model equation 14 predicts WSI with L/D, MC, and T (Table V). The very low R 2 value for the resulting model indicated that WSI may be controlled by various other factors such as residence time, extent of shear, etc., in addition to die dimensions, MC, and Tduring processing. Sinking velocity (SV) depends on the extent of expansion and, thus, the biochemical changes occurring inside the barrel. Extrudate expansion affects density of extrudates as well. Moreover, the extent of biochemical changes affect the water-absorption capacity and structural integrity of extrudates, which also affect the SV. The SV of the extrudates significantly (P < 0.05) decreased (35.4%) at higher T, indicating that the extrudates had a decreased UD and better buoyancy. Even though changing the MC of the ingredient mix had no significant effect on the UD of the extrudates, the SV of the extrudates obtained at 25% MC was significantly lower (16.3%) compared with the extrudates at 15% MC (Table II). The R2 value using L/D as the geometric parameter in the linear quadratic model was 0.84. Model equation IS predicts SV with L/D, MC, and T (Table V). The negative value for terms containing liD, within experimental boundaries, indicated that there was, in general, a decreasing trend in SV as the L/D ratio increased. Lower SV at higher MC and higher T is indicated by the negative coefficient for the MC and T terms in the model equation. TABLE IV (con:inuedfro,n previous page) Treatment Combination Effects on the Extrudate Propertiesa Property 90-100-100°C Die Diameter (mm) Water solubility index (%) 3.0 6.0 4.0 2.7 3.0 2.0 3.0 Sinking velocity (mis) 3.0 6.0 4.0 2.7 3.0 2.0 3.0 L8(-) 3.0 6.0 4.0 2.7 3.0 2.0 3.0 15% 3.3 3.3 3.4 4.8 5.8 7.3 10.0 3.3 3.3 3.4 4.8 5.8 7.3 10.0 3.3 3.3 3,4 4.8 5.8 7.3 10.0 3.0 6.0 4.0 2.7 3.0 2.0 3.0 3.3 3.3 3.4 4.8 5.8 7.3 10.0 3.0 6.0 4.0 2.7 3.0 2.0 3.0 3.3 3.3 3.4 4.8 5.8 7.3 10.0 b*() 20% 20% 25% 16.431322 17.16'° 0 na 17.1690 19 . 51 2418.37-57 1749 71416.6713 20 16.541422 18.3330 17.50' I9.07 17.99610 19 . 63 2417,16ho118 17.387-1117.9860 18.21 14.0523 17 . 8461!19,662.4 0.091113 nit 0 . 12 20,121.2 0 , 106.90.1 0 . 09 000.0911' 0 . 09 1200.091316 0.081822 008 19.22 0.092 13 0 . 09 100 na 45.29 4495 4.7 43.31712 42658.14 43357.11 44 . 615 84404610 46. 08 s 4348710 43,357.11 38.94 18-22 47.22' 90-140-140°C 90-120-120°C 46.38 4Q719.25 na 4.19 16-22 4.29'' 4.1417.22 4.18 16-22 4 . 01 2126 3.86 25-27 4.0220.26 422 15.21 5.23 2377' 3.962227 3 . 902327 0.111-1 0.113-1' 0.1 0.0169 0.1069 0.0719.23 0,109.12 35.622527 399016.19 36.9622.23 33.7027.28 36.4023.26 33.0428.29 31.6129 15% 17.96 6-10 na 17.4470 17 . 946 II) 17 . 02 1019 16261622 17121019 18.25 2016 1217.676' 18 . 03 31017131018 19.9323 21.14' na 0.13' 0.10' 009 13.18 0.0913-15 0 . 08 19.22 0.09 1.1 ' na 4.28 13-1 4.29 13 ' 389 24.27 4. 1017-24 4.6311 5Q92.4 4914.6 3 . 8026.27 14.4911.15 12.45 22-27 na 13.82' 15.541-314.822 12 o927-28 14.501 1-15 l5.09 12.11 25-28 14.15 14-18 14.961' 14.4711-1.512.25 25-28 15.5114 11.8328 14.50-15 15.05 12 o927-28 l4.94" 15.4215 na 15.80' 15.65' 14,885.12 15.25 15.29' 15.40' 16741220 16.65 13-21 15.6221 22 17.23" 16.72°° 16.321622 18644.6 0.0914-19 0.0720.24 0022.3 0.1224 0.108-11 00913.16 0.08 17-21 0.062932 0.0810.22 0.08 14-19 0.062529 0.07 21-25 0062630 0091' 43.856)0 na 46 . 162544435.9 46 . 292543996.10 45 . 523641.841 1-16 42700.13 45.62' 40.5915 8 40.65 14-18 42.8 1 8-13 48.70' 4.66" 4.0220.26 4091825 47369 43312.17 25% 4.25 15-20 4.0021.27 4.141 7.22 43113.18 43312.18 4431115 37.052225 40.51'" 390618.71 347926.28 35.822426 32.8628.29 34.562(28 4.27'' 4.1018-25 4.1317-23 4.4600 4.65" 5.272 13.91 16-19 14.67 14.0611- 16 140415.18 13.90169 l4.18' 15,331.6 15% 25% 20% 17.61613 na 17 , 308.1616.51 14-22 16 . 75 12211 15.5822 18 , 05 5.1016.8011.10 19.45 3 5 na 17636.13 17.37° 17 . 786 1117.05") 16.261622 16141922 16.07 19-22 16.21 17-22 17636.13 16.0719.22 15.85 20-22 0.0723.27 na 0 . 12 240,116.9 0 . 109200815' 0.053032 0.08" 0.07 22-26 cia 0.06 27-30 0.06 29-31 0.0816-20 0.0631.32 na 38.721 8-22 39.31 17-20 46.88' na 42.25 10-15 47,771.2 41391216 38.721822 36.052326 42.15'°° 41.15 13-17 41.1 1317 42.449- 15 4.15 17-22 na 4.80 4.63'' 4 , 85 5.85.521 4 00 1 " 4.27'' 4.25)520 na 4 . 28 14.19 4 50'° 13 3 . 8022743912.16 12.6122.27 na 13.7717-1914.3812- 16 14699.13 12.862224 11.8827-28 147383 12.34 13-28 na 12.4 123-28 14.751- 13 14.62912.95 21-23 14.0615-18 14.5210-15 14.3812-16 13.4719-21 14.5210-1.5 14.27130 14.0415-18 0.04 0.l0'° 0.072025 0.09 00624.28 0.06 0 344526.28 35372527 37.0921 .24 37.9219.22 39171720 35.2825.27 37.65 20-23 4.7069 5152.3 4.76 4.3212.18 4,539.11 4.50 10-14 4,519.12 12652226 14.24'' 13.8916-19 13.1420-22 13.6218.20 12.2724-28 127122.25 with the same superscript numbers for a given property are not significantly different (P < 0.05); na, data not available. Vol. 84, No. 4, 2007 393
  • 6. Color change in extrusion processing is mostly due to Maillard reactions (Mercier et al 1989). In fact, significant losses of lysine (an important ammo acid required for fish growth) during" sion processing (Bjorck and Asp 1983) have been observed due to Maillard reactions. Extrudates obtained at a T of 140°C had lower brightness (L) and yellowness (b) values, but had a higher redness (a) value (Table II). A similar trend was observed by Shukla et al (2005) during extrusion experiments with raw materials that also contained DDGS. This may have been due to Maillard reactions, which resulted in the browning of extrudates at higher temperatures. Increasing the MC from 15 to 25% resulted in a 22.9 and 18.5% decrease, respectively, in brightness and yellowness, hut a 7.0% increase in the redness of the extrudates. In general. extrudates obtained with higher MC had lower brightness and yellowness values and higher redness values. This might have been due to the higher resulting temperature of the ingredient melt at the die (Table Ill), which may have contributed to the browning. Changing the die dimensions also had a significant effect on resulting color values: model equations 16, 17. and 18 (Table V) predict the color of the extrudates with L/D. MC, and T (R 2 for I. = 0.70, R 2 for a = 0.29, and R 2 for b* = 0.76). Within the scope of the experiment, the positive value for the term containing L/D in the model indicated that there was a general increasing (rend in L as the L/D ratio was increased. Similarly, a positive value for the term containing L/D in the model indicated that there was an increase in a as the LID ratio was increased. On the other hand, the negative coefficient for the L/D term in the model for b* indicated that there was a decrease in h as the L/D ratio was increased. Extrusion Processing Parameters Mass flow rate (MFR) in a single-screw extruder depends on the drag flow developed by screw rotation and the pressure flow developed due to the restriction of the die (Mercier et al 1989). In this study. increasing T from 100 to 140°C resulted in a significant increase (3.9%) in the MFR (P < 0.05). On the other hand, increasing the MC from 15 to 25% resulted in a 32.5% decrease in the MFR. The R 2 value using LID as the geometric parameter in the linear quadratic model was 0.87. Regression equation 19 predicts MFR using L/D, T, and MC (Table V). A negative coefficient for LID in the model indicated that there was a decreasing trend in MFR as the L/D ratio was increased. The decrease in MFR with higher MC is explained by the coefficient (18.42_O.6* MC) for MC term in the model. The higher MFR at higher Tcan he explained by the positive coefficient for Tin the resulting model. Dough Temperature The temperature development inside the barrel depends on thermal gradients, thermal conductivity, thermal diffusivity, degree of mixing, velocity of flow, etc., and ultimately affects the extrusion process as well as the resulting extrudate properties. Increasing T from 100 to 140°C resulted in a 23.60% increase in TB, which compared with a 49.1% increase in TD. In the extruder used, the die section did not have a compressed air cooling system, which contributed to the increase in TD. The pressure and shear developed inside the die may also have contributed to the higher TD. Increasing MC of the ingredient mix resulted in a significant (P < 0.05) decrease in TB, while the reverse was observed for ID (Table LII). The R 2 value of the Linear quadratic model with L/D as the geometric parameter in the TB prediction model was 0.73. The R 2 value to predict TD was 0.97. The resulting TB prediction equation 20 uses L/D, MC. and T (Table V). The negative value for the L/D terms indicated that there was, in general, a decreasing trend in TB as the L/D increased. A negative coefficient for MC in the model indicated that the TB decreased as the MC was increased, whereas a positive coefficient for the T term indicated that the TB increased as Tincreased. Regression equation 21 predicts ID with LID. MC , and T(Tahle V). A negative coefficient for the IJD term in the model indicated that there was a general decreasing trend in TD as the LID ratio was increased. On the other hand, a positive coefficient for the MC and T terms in the model indicated that there were general increasing trends in TD as the MC and T were increased. In our experiment, we observed that increasing the temperature profile in the barrel resulted in increased TD and TB (Table IL!) leading to a reduction in UD, BD. PD, SV. L, and an increase in WAI and a* of the extrudates (Table II). However, increasing the moisture content of the ingredient mix resulted in reduced TD but increased TB of the molten dough. Absolute Pressure (P) The pressure developed inside the die depends on various parameters such as rheological properties of the ingredient blend and pumping characteristics, in addition to the die dimensions used in the extruder. The biochemical conversions occurring inside the barrel depend on the extent of pressure developed inside the extruder, in addition to the extent of thermal and mechanical energy available for chemical reactions, and ultimately affects the extrudate properties. Increasing the T resulted in a significant decrease in the P developed in the die (P < 0.05). In foct, increasing T from 100 to 140°C resulted in a 50.6% decrease. Moreover, at TABLE V Regression Models for Extrudate Properties and Extrusion Processing Parameters Using Moisture Content (MC), Barrel Temperature (T), and Length-to. Diameter Ratio of I)ie (L/D)a Eq Property to UD BD PD WAI wsI sv L* a* Regre.ssion Model R2 SE CV(%) 1.141+0003 *(IJD)-0.025 * MC +0.018 * T-O.003 *(LJD)*MC 0.65 0.098 10.0 -0.63 + 0.0104 * (UD) + 0.022 * MC + 0.01 6 * T+ 0.002 * (LID)2 - 0.003MC2 0.62 0.025 5.7 t2 t39.78- l4.93 *(UD)-2.3t *MC- lIT *T_0.33*(IJD)*MC+004*T*MC_054*(LID)2 0.69 6.87 7.4 13 0.99-0.02 * (LID) + 0.03 * MC + 0.01 * T 0.65 0.176 6.? 14 12.41 +0.57 *(IJD)-0.25 *MC+0.14 *T+0.002(1JD) T-0.017 *(UD)* MC+0.002 * T*MC 0.4 I t.to 6.3 l5 0.934-0.084 * (UD) - 0.005 * MC - 0.002 * T + 0.006 * (LID)2 0.84 0.044 15.4 16 16.62 + 1.77 *(UD)+ 3.21 * MC -0.03 * T- 0.09 *(LID) * MC -0.09 *(MC)2 0.70 2.36 5.7 17 2.42 + 0.14 * (LID)- 0.03 * MC + 0.02 * T- 0.003 * (LID) * T+ 0.0l * (L/D) * MC 0.29 0362 8.2 l8 27.86-0.03 * (LID) -0.67 * MC -0.07 T + 0.004 * T MC 0.76 0.520 3.7 19 MFR 3.95-0.20 *(tJD)+ 18.42 * MC + 0.17 * T-0.60 * MC2 0.87 9.33 6.6 20 TB 60.t4 - 0.710 * (L/D)- 0.229 * MC + 0.390 * T- 0.04 * (UD) * T- 0.259 * (L/D)2 0.73 6.43 5.6 21 TD -30.38-0.41 *(LID)+ 0.48 * MC+ 1.27 * T 0.97 3.98 3.1 22 P 173.7- 0.64 * (LID)- 1.27 * MC - 14.0 * T- 0.03 *(L/D) * MC+0.09 * T* MC -3.0 * (JJTJ)2 0.86 1.58 19.2 23 SME -2 t 90 + 58.3 * (LID) + 282.6 * MC - 3.16 * T - 3.03 * (LID)2 - 7.04 * MC2 0.56 tO 1.8 27.7 24 -447.9 + 3.26 * (L/D)+ 59.6 * MC -0.47 * T- 1.53 * MC2 0.71 15.3 23.8 25 -34049 + 1134.9 * (LID) +4049 * MC- 18.8*T_2 . 2 * (LID) * T- t53*(LJD) * MC-26.5 * (lJrJ)2_ 102.3 * MC2 0.71 101.7 23.8 UD, unit density, BD, bulk density; PD, pellet durability; WAL, waier-soluble index; WSI, water-soluble index; SV, sinking velocity; L* . brightness. a*, redness, b*, yellowness, MFR, mass flow rate; TB, temperature of dough at the barrel; TD, temperature of dough at die; P, pressure developed in the die; SME, specific mechanical energy; Q. torque; ii, viscosity of dough. 394 CEREAL CHEMISTRY
  • 7. higher T, the apparent viscosity of the ingredient melt decreased (Table 111). Thus the ingredient melt at lower viscosity might have resulted in decreased P inside the die. Lam and Flores (2003) observed a similar trend during extrusion of fish feed. Increasing the MC of the ingredient mix also had a significant effect on the P developed in the die. The P at 15% MC was 63.7% higher compared with the P at 25% MC. The R 2 value using L/D as the geometric parameter in the linear quadratic model was 0.86. Model equation 22 predicts P with L/D, MC, and T (Table V). Within the bounds of the study, the coefficient for (LID ) 2 in the model was significant indicating that P had a nonlinear relationship with LID. The reduced P inside the die at higher T is indicated by the negative value for the terms containing T in the model. Increasing the temperature profile in the barrel as well as increasing the moisture content of the ingredient blend resulted in reduced P (Table Ill) leading to decreasing trends in UD, BD, PD, SV, L*, and increasing trends in WAI and a (Table 11). Specific Mechanical Energy (SME) In extrusion processing, the amount of biochemical reactions occurring inside the barrel depends on the thermal and mechanical energy available. To induce optimum conversion of the ingredients to obtain extrudates of high quality, appropriate combinations of shear and thermal energy are very important. The amount of TABLE VI Treatment Combination Effects on the Extrusion Parameters' Property Die (mm) LID (-) 15% 20% 25% 15% 20% Mass flow rate (g/min) 940252s na 157.45 11 na 1 48.9° ia 3.3 3.0 55 7.14 152 4814 165.079 31.21" 158.8" 3.3 6.0 81.326 I56.3"° I70,9'' I57.9'13 163.529 34 4.0 I 56.7' 99.62425 157.5' 1 173.71-4153,30.14 158.7'' 4.8 2.7 553711 151.8814 109,52024 I50.9''' 158.0 ° 5.8 3.0 146212.14 100.221156.0 163.4''° 0A' 2.0 144.01215 166.118 100,572.25 147,11114 154.4''° 0.0 3.0 Torque (N-rn) 3.0 6.0 4.0 2.7 3.0 2.0 3.0 3.3 3.3 34 4.8 5.8 73 10.0 SME (Jig) 3.3 3.0 3.3 6.0 3.4 4.0 4.8 2.7 5.8 3.0 7.3 2.0 10.0 3.0 Apparent viscosity (Pa-sec) 3.3 3.0 3.3 6.0 3.4 4.0 4.8 2.7 5.8 3.0 7.3 2.0 10.0 3.0 Absolute pressure (MPa) 3.3 3.0 3.3 6.0 3.4 4.0 4.8 2.7 5.8 3.0 7.3 2.0 10.0 3.0 Dough temp barrel (°C) 3.3 3.0 3.3 6.0 3.4 4.0 4.8 2.7 5.8 3.0 7.3 2.0 10.0 3.0 A,. i°C Un.. 5 Ong 3.0 60 4.0 2.7 3.0 2.0 30 3.3 3.3 3.4 4.8 5.8 7.3 10.0 Ila 48.21922 58.415- 1 R 81.2811 68.212-14 74.9'0 11 91 90.7 102.7-1-429.6"° 30.12830 95 345 29.72830 100 745 41,322.27 107.214 104.22141,622.27 III 313 115.3' 107.6' 441 , 4 22.27 563.0" na 247 . 8 2(25501.6' 520.868 291 , 8 18.22 381 . 7) 2.14570.9' 547.8' 352.5'''' 576.3' 338.8''' 485 . 8 810596.9' 6788.0' na 6298.9' na 5367.5 11 7087.1 1-4 3862 . 3 1518 6658.7' 7623.9' 4948.5" 6888.324 4509.0°" 6073 . 4677l09.7" na 492 2125 I3.07 l9.2 18.93 , 39479 27.68' 8.1014 5.16 20 6.67'' I 10,47)112 15.3556 17.14 102.82124 na 10172325 J01.6 23 25 103.121-24 104 . 9 19.2 ) 108 . 1) 7 ( 8102.92)24 102.522-24 105.5 19-20 106 . 8 1819102.92124 108 . 8 .18103.2 21 23 na 101,223.27 102,422.27 l04.3223 101 923 .27 101,025.27 100.62627 90-140-140°C 90-120-120°C 90-100-100°C no 50,818.21 53916.19 61,9117 34.12730 68.214 82,181 256.82024 no 187 , 5 27251,42(1.25 298 . 5( 20257.52024 318.4 1 ' ° 338.8'' °' 194.6 310.5 15-1 626 . 2 2 .3 357.2''° 3359(512 4035' 12 25% 1()1.821-21 121 I620 I l9.9'"° 104.02125 II 115.819-22 127.916 8 4941922 34 ITh' 730H 7331113 3592529 88.160 3532829 95.0156 83.97-938.32328 104.42-444.62125 46,120.24 105.524 256.3 20 21 392.8' 2-3 460.1 9 10 492.5' '° 45I.10' 624.62.3 597.831 273.41823 490.88)0 244322.25 277.4(7.23 264.51924 314.3 15-18 3266.0(9.22 2253.627.31) no 1954.3 29 10 3357,91821 1991.52830 4846.4 14828.5'"° "° 2336.020.29 6280.456 2728 , 42 2.224091.6°' 2371.425.29 1965 , 2 28303563.1 17.20 5822.6 6898 . 4 242946.5225 4511.112.14 7359.8 " 2533.42328 2255 . 8 27.305544.O' 2753. 122 21 2733 . 8 22275427 . 08 ( 06970 , 4243049.021.24 4 . 05 2326 flu 2 . 88 2629 6.9211- 18 3.37 24-29 8 l5'' 3,7979 629)8.20 6 . 04 1821 10.34° 14.961-714.3968 20,572 8.02'' 103 , 920.22 na 9932628 110.816 101 , 423.26 118.611-11 119.88.9 97 .928 99 . I 27118.38-11 119.38.10 101 , 623.27 120.0' 99.65 25-28 104.42123 109.3' 102 . 1 232799.82 105,220.22 103,12226 106,719.21 107.8'° 104.521.23 1039 21.24 102 . 62227103.62225 114.418 102 , 922.2) 3,942327 3.62 23-28 4752)25 8.97 7.72'' 13.5589 12.8290 117.1(0.14 115.91214 I 17 . 3 (014 118.01° I l6.7°' 117.410- 1 116.91 2.44283) 6.75 16-19 2.0929.32 4.08 23-26 4.31 22-25 7.07' ° 6,97(5(8 I l6.9°' 113.5° 11561315 117.79-11 115,314.15 I5.7°'° 1l5.515 136.811 143.4" na 128.513(6 127.1(6 123.617 130.312-15141.410 129.8)1.16 138.01' 131.412' I30.8°'' 129.913.16 128.91-1-t6129.3' 127.715-16 127.2 16 128.414-16130.5(2.15 127.08 15% 20% 140.6 ° 155.87 ' 161.1312 153,9814 147.311-14 ° na 177 . 0( 2163.22 1 ° 161.8 ' 169.0" 172.2 1 ' 176.1 5 flU 42.9212), 46.42024 112.6' 2 47.81922 n 694)2(4 67.1 '' 63.6 14-1 75.99 (2 53.6 17-20 9435.8 91.16-7 n 203.2 25- 27 215.2 24 27 289.5)7.21 n 319.915-18 324.3°' (8 653.6' 250.31' -25 322 5°'° 402.9' '-' 297.2(0.20 471 .8' '° 459.8' '° 25% II47(9.21 130.4°' 123.616 1 110 19.24 l6.622 104,62025 11661722 25.9311 30.7 28-10 30 9281)) 32.120.1)) 34 12738 38.1 2 .29 37.4 24-29 184.6 191 . 926 27 203 .911-27 237.3 24-27 238.423 . 26 297.6 16-20 262.3'' 1716.00 744l.1" na 2026.82030 2832 . 921263157.1 19-22 2122.82830 5020.5'' 3672.7" 2040.72830 3068 . 2 2023 4206.8'"' 2520.123.28 6234.4 5-6 4585.8° " 35444)7.20 2250.927.30 no 6023 , 60.72476.724.29 4438.0' -' 4332225 na 1.363072 2 . 6827.30 2.142932 3 . 91 2327 6.55'" 10.431 1-12 3.882327 na 12 . 799109.92i2 I0.15° " 15.92 136.8' na 100 , 8 24.27 93.529 132. 1 2-5 133. 12-4 133 . 92l32.9 131.638 na 133 . 5 24131.63.6 131446 13372 3 na 151.58 156.1' 155.9 na 152.7 150.9 154. 947 152.078 155.7 155.2 l55.7' 152.468 150.30.9 1.18' 0.9432 1.3 131-32 2.902529 53032 4.922)'25 5491922 124.8 110.116.17 132.32.5 132.22.5 130. 11-6 129.66 13144.6 170.7' 156.1 153.05.8 158.523 160.22 159.32 147.49 Values with the same superscript numbers for a given property are not significantly different (P < 0.05); na. data not available. Vol. 84, No. 4, 2007 395
  • 8. TABLE VII Correlation Coefficients for All Multivariate Extrusion Data,h D D L LD T MC UD WAI wsI BE) PD sv MFR SME ii a. I, TB TI) 0.174 -0.541' 0.007 -0.028 -0.177 0.011 -0.090 0.509' -0.405' 0.676' 3234' 0.117 0.270* -0.193 0.116 -0.039 0.257 -0.43)' -0.318' -0.042 IM 0.716* -0.001 -0.076 0.128 -0.164 0.226 0.105 -0.036 0.087 0.098 0.095 0.073 0.110 0.173 0.029 0.182 0.337* -0.062 -0.087 LI) -0003 -0.057 0.242* -0.164 0.242' -0.247' 0.255* -0.380' 0.274' 0.021 (1.272* 0.243* 0.038 0.096 --0.0)0 0.60Y 0.150 -0.053 T 0.028 0.489* 0.693* _0,223* -0.368' -0.332' -0.499' 0.277* 0.089 -0.316' -0.231 * -0.112 0. 203 * -0.022 -0.392' 0.813' 0,976* MC LSJJJ WAL wsI 0.074 0.383* -0.492' 4)0887 0.380* -0.221 -0.345' -0.875' -0.017 -0.294° _0.76l* 0.298' -0.839" 4)567* -4)063 0.12) 4)414* 0.16) 0.372' 0.459* 1)162 0)77 -0.122 0.249' 0.141 -0.024 0.0)3 -0.062 0,314* -0339' -0.471' 473* -0.334' 41.125 0.48l* -0.387' -0.287' _0,299* 4)333* -0.387' 0.211* -4)384' -0.566 0.552' 0.727* 0.007 0.02 0.099 0.307' 0,380* 0.186 0.283* 0.531* -0.308' 11.480' 0.498' -0.084 -0.282' BD -0.068 0.715' -0.038 0.064 -0.078 -0.056 0.079 0.047 0.188 -0.048 -0.462' -0.389' PD -0.255' 0.111 -0.384 0.210' 0.077 -0.096 -0.156 -4)272' 0.2)7 -0.033 -0.278* (continued on next page) D. diameter of die nozzle. 1.. length of (lie nozzle; liD. liD ratio of die nozzle; T. temperature: MC, moisture content of ingredient mix; UD. twit density: WAI, water-absorption index, WSI, water-solubility index: BD, hulk density: PD. pellet durability: SV, sinking velocity: Q. torque: MFR. mass flow rate; SME. specific mechanical energy. t. apparent viscosity: I. e. brightness; a. redness; 6'. yellowness; P. absolute pressure in the die; TB, temperature of ingredient nix at the barrel; TD, temperature of the ingredient mix at die. '. Significant at P <0.01. mechanical energy applied to the ingredient mix is measured in terms of SME. SME is the net amount of energy utilized by the extruder to produce unit mass flow rate of the material. In singlescrew extrusion, it is very difficult to control the SME because the material is transported by friction between the screw and barrel surfaces and the material. At higher T, SME decreased; increasing T from 100 to 140°C resulted in a 28.8% decrease in the SME. The reduced SME consumption at higher temperature profile in the barrel resulted in decreasing trends in UD, BD, PD, SV, L*, and increasing trends in WAI and a' value. The MC also had significant effect. The highest SME (653.6 JIg) was observed at 20% MC, while the lowest SME (184.6 JIg) was observed at 15 and 25% MC (Table VI). As expected, die dimensions also had a significant effect. The R2 value with L/D as the geometric parameter in the linear quadratic model was 0.56. Model equation 23 predicts SME with LID, MC, and T (Table V). The (LID) 2 term in the model indicated that there was a nonlinear trend between SME consumption and LID ratio. A negative coefficient for T in the model indicated that there was a decrease in SME as T was increased. MC also exhibited a nonlinear relationship with SME, as indicated by the MC 2 term in the model. Torque (U) In general, most food and feed materials exhibit pseudoplastic behavior. As the screw speed increases, viscosity decreases, which affects the torque requirement. Reduced viscosity at higher shear rates affects the mass flow rate as well. Mass flow rate also affects the torque requirement. Hence, U is an important parameter in extrusion processing, and ultimately affects the quality of extrudate properties. Increasing T resulted in a decrease (P < 005) in the U required to operate the extruder (Table Ill). In fact, increasing T from 100 to 140°C resulted in a 33.9% decrease in U. This behavior occurred, at least in part, because increasing T resulted in a reduced apparent viscosity (Ti) of the dough, which thus required less torque to rotate the screw. The decreased torque requirement at higher temperature profile in the barrel resulted in reduced UD, BD, PD, SV, L*, and increased WAI and a' values (Table III). Changing the MC also had a significant effect on the U required to operate the extruder. Maximum U was required at 396 CEREAL CHEMISTRY 20% MC, and increasing or decreasing the moisture content from 20% resulted in reduced U. Changing the die dimensions also had a significant effect on U. The R2 value with L/D as the geometric parameter in the linear quadratic model was 0.71. Model equation 24 predicts U with LID, MC, and T (Table V). A positive coefficient for the L/D term in the model indicated that there was, in general, an increasing trend in U requirement as L/D increased. A negative coefficient for T in the model indicated that the U requirement decreased as the temperature was increased. Apparent Viscosity (i) Viscosity development inside the barrel depends on ingredient composition, constituent molecular weights, processing temperatures, pressures developed, and thermomechanjcal history, and affects the final product properties (Gagos and Bhakuni 1992). Apparent viscosity can reveal several of these parameters and thus is often used to monitor product quality online. Increasing T from 100 to 140°C resulted in a 33.9% decrease in the r inside the barrel. Due to this decreased r], there was a decreasing trend in extrudate properties such as UD, BD, PD, SV, and an increasing trend in WAI and a' value was observed (Table II). As expected, changing the MC of the ingredient mix also had a significant effect on i Maximum Ti was observed at 20% MC. Changin g the die dimensions had significant effect on ii as well. The R2 value to predict Ti with L/D was 0.71. Model equation 25 predicts Ti using L/D, MC, and T (Table V). The negative coefficient for the T term in the model indicated that there was a decrease in apparent viscosity as Tincreased. The (LID) 2 and (MC) 2 terms in the model were also significant, indicating that the LID of the die and MC had a nonlinear relationship with Ti of the ingredient melt inside the barrel. Correlation Analysis After examining individual treatment effects, as well as treatment combination effects, the multivariate data were subjected to correlation analysis to further examine relationships between the variables. The Pearson correlation coefficient r provides the strength of linear relationship between two variables (Rao 1997). In this study, high correlation coefficients occurred between some a priori
  • 9. TABLE VII (continued from previous page) Correlation Coefficients for All Multivariate Extrusion Dataa sV ri MFR -0006 0.143 -0.033 0.008 0.233* -0.149 0.288* -.1)027 -0.643* -0.532' 0.468 0.890 0.956* 0,464 _0.284* 0.398* 0.575° -0.095 .0350* 0.074 0.409* 0.721* .0.205* 0.844* 0.414° 0.119 -0.018 0.9l6 0.186 .40236* 0.055 0.453° -0.156 .0356* TB a SME TD D L LD T MC UD WA! Wsl BD PD sv MFR SME 11 L5 a b5 P TB TD I 0.462k _0.347* 0.354° 0.530* 4)070 .0299* I -.0,672* 0.832° 0.531 0.066 -.0.202* -0.226° .40323° 0.016 0.229° I 0.454° 0.025 -0.132 I -0.129 -0463° 0799° LID ratio of die nozzle; T. temperature; MC, moisture content of ingredient mix; 1.JD, unit density; WA!, D. diameter of die nozzle: L. length of die nozzle; LID. torque: MFR. mass flow rate, SME, specific water-absorption index; WSI. water-solubility index: BI). hulk density: PD. pellet durability; SV. sinking velocity; D, h* . yellowness: P. absolute pressure in the die; TB. temperature of ingredient inix at the r, apparent viscosity; l.°. brightness; a°, redness: mechanical energy: barrel: TD, temperature of the ingredient mix at die. . Significant at P <0.01. expected pairs of responses; some were not anticipated, however. The temperature profile in the barrel was adjusted to control the extent of heat treatment applied to the dough during processing. The nature of thermo/cheinical/mechaflical changes occurring in the ingredient mix affects the viscosity of the dough that develops, which thus affects the extrusion processing parameters. Hence, we expected strong correlations between barrel and dough temperature, between die and dough temperature, and between apparent viscosity, torque, and SME. As anticipated, several of these correlation coefficients exhibited very strong relationships, with absolute r values >0.90 (P < 0.01) (Table VII). The independent variables controlled in our experiments will affect the extruder processing conditions, which in turn will affect the extrudate properties. Hence, we expected good correlations between the processing conditions and extrudate properties. As anticipated, mass flow rate and moisture content, WAI, and dough temperature at the die, sinking velocity, and dough temperature at the barrel, apparent viscosity, and die pressure, sinking velocity, and dough temperature at the die, and bulk density and die diameter had correlation coefficients with an absolute value >0.70. It was also anticipated that correlations between extrudate properties such as bulk density, unit density, sinking velocity, and color would occur. As expected, the correlation between bulk density and sinking velocity, unit density, and sinking velocity, L* and a* had correlation coefficients with absolute values >0.70. Additionally, the color of the extrudates exhibited correlation with extrusion processing parameters: mass flow L*, rate and L*, mass flow rate and b*, water-solubility index and L* all were significant, with correlation coeffidie pressure and cients with absolute values > 0.6. These correlations may have the potential for predicting extrusion processing conditions and extrudate properties and should be further investigated. CONCLUSIONS The goal of this study was to investigate the effect of die nozzle dimensions, barrel temperature profile, and moisture content on DDGS-based extrudate properties and extruder processing parameters. All of these factors had significant effects on extrudate properties such as unit density, bulk density, pellet durability, water absorption index, water solubility index, sinking velocity, and color, and extrusion process ingparameterS such as the mass flow rate, dough temperature, absolute pressure, specific mechanical energy, torque, and apparent viscosity. Increasing the moisture content from 15 to 25% resulted in decreases of 2.0, 16.0, 16.3, 22.9, 18.5, 32.5, and 63.7%, respectively, in bulk density, water solubility index, sinking velocity, L*, b*, mass flow rate, and absolute pressure, but an 11.6, 16.2, and 7.0% increase, respectively, in pellet durability, water absorption index, and a* . On the other hand, increasing temperature from 100 to 140°C resulted in decreases of 17.0, 5.9. 35.4, 50.6, 28.8, 33.9, and 33.9%, respectively, in unit density, pellet durability, sinking velocity, absolute pressure, specific mechanical energy, torque, and apparent viscosity, but a 49.1 and 16.9% increase, respectively, in dough temperature and water absorption index. It was also determined that, using a linear quadratic model, the L/D ratio of the die, along with moisture content and temperature of the transition and die sections, predicted well most of the extrudate and extrusion properties studied. The aim of this study was to investigate extrusion processing of a 40% DDGS aquaculture feed blend on a laboratory scale, as a precursor to scaling up to commercial equipment. Ultimately, production of these types of feeds on a larger extruder may change the interactions observed with this study, but we have examined a wide range of parameter settings, which will be useful for scale-up purposes. Future studies will examine other levels of DDGS as well. ACKNOWLEDGMENTS We thankfully acknowledge the financial support provided by the Agricultural Experiment Station, South Dakota State University, Brookings, SD, and the North Central Agricultural Research Laboratory, USDA, ARS, Brookings, SD. LITERATURE CITED Alves, R. M. L., Grossmann, M. V. E., and Silva, R. S. S. F. 1999. Gelling properties of extruded yam (Dioscorea alota) starch. Food Chem. 67:123-127. Vol. 84, No. 4, 2007 397
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